Initial Configuration

The neutron star obeys a polytropic equation of state, P = Kρ0 Γ, at t = 0. It is evolved according to the adiabatic evolution law, P = (Γ-1)ρ0ε, where P is the pressure, K is the polytropic gas constant, ε is the internal specific energy, Γ is the adiabatic index, and ρ0 the rest-mass density. We chose Γ = 2 to mimic stiff nuclear matter. This star is irrotational (nonspinning) and in a quasiequilibrium circular orbit.

Black Hole

For the spinning BH we consider the mass ratio q = MBH/MNS = 3. It is spinning rapidly, with SBH/MBH2 = 0.75.

Neutron Star

The initial compaction of the neutron star is MNS/RNS = 0.145. The rest mass is 83% of the maximum rest mass of an isolated, nonrotating NS with the same polytropic EOS. It has a radius of RNS = 13.2 km (M0/1.4 Mʘ) and a mass of MNS = 1.30 Mʘ (M0/1.4 Mʘ). In the cases where the neutron star has a magnetic field, Bmax ~ 10   17G and ⟨ B 2/8πP ⟩ = 0.005.


The initial binary is in a quasiequilibrium circular orbit, and has a frequency of MΩ = 0.032. The initial coordinate separation is D/M = 8.80. The matter and gravitational field variables are determined by using the conformal thin-sandwich formalism. BH equilibrium boundary conditions are imposed on the BH horizon.

The metric (gravitational field) is determined by integrating the Einstein field equations according to the BSSN prescription. The matter and electromagnetic fields are evolved by solving the equations of relativistic hydrodynamics via a high-resolution, shock-capturing (HRSC) scheme.

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